The Verizon SDWC property is a separate remediation site. A Site Characterization Report indicating closure via a combination of Statewide Health and Site Specific Standards was submitted by the property owners and approved in 2012. A subsequent SSS Remedial Action Plan was approved in 2012. A Remedial Action Completion Report was submitted in 2015, in which they requested closure via a combination of Statewide Health, Site Specific, and Background Standards due to impacts at the southern property boundary which is across Maiden Lane from the then refinery.
Groundwater gradient in the area between the Verizon property and the area of the remediation system along Maiden Lane is shallow but we generally observe a groundwater flow pattern that indicates convergence in the vicinity of the AOI 8 boundary with Maiden Lane, near the Mifflin Street Sewer.
The benzene dataset presented in Figure 9-2 of the AOI-8 RIR utilized maximum concentrations from 2014-2016 groundwater sampling, as this was the most comprehensive dataset at the time. It should be noted that benzene concentrations measured in groundwater varied through that time period (as low as 6.2 micrograms per liter (ug/L) in a V-MW-9 groundwater sample on 3/16/16; benzene was not detected in well N-3 groundwater samples on 6/2/14, 3/17/16, and 5/27/16; benzene was not detected in well V-MW-16 groundwater samples on 4/17/14, 6/25/14, 9/5/14, and 3/16/16 (See AOI 8 RIR Table 4-2). An overall decreasing benzene trend in this area was demonstrated in the RIR in Figure 9-5b.
Subsequent gauging and sampling supports the RIR interpretations of groundwater flow patterns in this area and indicates recent N-3 benzene concentrations ranging from non-detect to 6.75 ug/L in groundwater. The area wells will continue to be monitored and data will be incorporated into future modeling efforts.
A horizontal recovery well was installed in that area for the purpose of LNAPL recovery as well as to mitigate any potential migration of dissolved contaminants away from AOI 8. The treatment system in that location was started up in January 2021. Therefore, you would not have seen any changes in the groundwater gradient as a result of pumping in reports submitted prior to that time.